1. Field of the Invention
The present invention relates to a lens having a power zooming function and a camera. More particularly, the invention relates to a technique to miniaturize and lighten a lens barrel as well as to implement an effective utilization of the auto-focus driving unit in a camera body using a driving unit for focusing installed in the camera body as a driving unit for the power zooming, for example.
2. Related Background Art
FIG. 1 illustrates the structure of a conventional auto-focus camera schematically. The apparatus shown in FIG. 1 comprises an exchangeable zoom lens barrel 117 and a camera body 32. In the zoom lens barrel 117, a motor 118 for driving the zooming lens group and a motor 114 for driving the focusing lens group are provided. Then, in response to the operation of a zooming switch 111, the driving power of the aforesaid zooming switch 111, the driving power of the aforesaid zooming lens group driving motor 118 is transmitted to a zooming cam barrel 104 through a pinion gear 110 to rotate the aforesaid zooming cam barrel 104 for the execution of an electrically driven zooming operation. Also, the driving power of the focusing lens group driving motor 114, which is another motor independent of the aforesaid zooming lens group driving motor 118, is transmitted to the focusing cam barrel 107 through a pinion gear 115 to rotate the aforesaid focusing cam barrel 107 for the execution of an electrically driven focusing operation.
In this respect, the driving signals for driving the focusing lens group driving motor 114 are generated by a CPU 116 in the lens to which the control signals generated by a metering photoelectric conversion unit 30, focusing control circuit 31, and others in the camera body 32 are inputted. Also, in the camera body 32, a focusing motor 22 and others are provided for a lens of a type in which no motor is installed for driving the focusing lens group.
Also, FIG. 2 illustrates another example of the structure of an auto-focus camera having a conventional power zooming function. In this camera, no motor for driving the focusing lens group is provided in the zoom lens barrel 217. Its focusing is performed by a focusing driving motor 22 in the camera body 32. In other words, the driving power of the motor 22 in the camera body 32 is transmitted to gears 23 and 21a, a driving shaft 21, and a coupling unit 21b on the camera body side. Then, from the aforesaid coupling unit 21b, the power is transmitted to the focusing cam barrel 207 through a coupling unit 219b on the lens side, a coupling shaft 219, and a gear 219a to rotate it for the execution of an electrically driven focusing operation.
Also, regarding the zooming operation, the driving power of the zooming lens group driving motor 218 which is provided in the zoom lens barrel 217 is transmitted to a zooming cam barrel 204 through a pinion gear 210 in response to the operation of a zooming actuation switch 211 as in the case of the embodiment described in conjunction with FIG. 1, and the aforesaid zooming cam barrel 204 is caused to rotate for the execution of an electrically driven zooming operation. In this respect, the signals for driving the focusing motor 22 on the camera body side 32 is generated when the focus driving control signals, which are obtained by a photoelectric conversion unit 30, focusing control circuit 31, and others, are inputted into a CPU 216 in the lens barrel 217. Thus, the CPU 216 controls the focusing motor 22 on the camera body side 32.
Also, in the above-mentioned apparatuses according to the prior art, the one shown in FIG. 1 is provided with the focusing lens group driving motor in the lens barrel to perform a high-speed focusing for various types of lenses. However, as a zooming lens group driving motor is mounted in the same lens barrel, there are disadvantages that the lens barrel becomes large and its weight becomes inevitably heavier. Also, when a zoom lens barrel such as this is used by mounting it on the camera body in which a focusing lens group driving motor is installed, the focusing lens group driving motor provided for the camera body does not render any service at all. This is obviously inefficient.
Also, in a case of the conventional auto-focus camera system, as shown in FIG. 2, where its focusing lens group is driven by the use of a focusing lens group driving motor in the camera body through the mechanical coupling, it is necessary to provide a motor and its driving mechanism in the lens barrel only for the purpose of driving the zooming lens group. In this case, too, there are disadvantages that the lens barrel becomes large and its weight becomes heavier.